Answer:
Our Constitution is based on certain principles
.
Explanation:
The term <em>principle</em> is a noun and it indicates <u>fundamental beliefs that something is based on</u>, whether it be a <em>constitution</em> in this case, or <em>somebody's beliefs</em>. <em>Scientific principles</em> are the <em>laws of science</em>.
The correct use of the word in other sentences would be:
Our experiment was based on scientific <u>principles</u>.
The <u>principles</u> of my parents have always stuck with me.
On the other hand, <em>principal </em>is an adjective and it refers to something that is primary, main. It can also be used as a noun: The <em>principal </em>visited our class today. In this case, it refers to the <u>headmaster of a school.</u>
